Transducers for transmitting and/or receiving ultrasonic energy

ABSTRACT

Improved ultrasonic energy transducers each include a material contacting member secured to a piezoelectric element at an interface region between oppositely operated first and second regions of the piezoelectric element. The material contacting member intensifies and amplifies movement of the interface region as the first and second regions of the piezoelectric element operate in a push-pull mode relative to the interface region. The first and second regions of the piezoelectric element can be electrically driven to move the material contacting member for transmission of ultrasonic energy or mechanically driven by the material contacting member for receipt of ultrasonic energy. A variety of piezoelectric elements can be used in the improved transducers including, for example, generally rectangular bars and discs segmented into two or more portions. A variety of material contacting members can also be used including, for example, a cylindrical stud and a more narrow dowel.

This is a division of application Ser. No. 08/010,652 filed Jan. 28,1993 U.S. Pat. No. 5,398,538.

BACKGROUND OF THE INVENTION

The present invention relates generally to on-line measurement ofproperties of sheet material as the sheet material is being manufacturedand, more particularly, to methods and apparatus for measuringmechanical properties of webs of sheet material as the webs are beingmanufactured by measuring the propagation speed of ultrasonic energythrough the webs. While the present invention can be applied to webs ofa variety of materials, it is particularly applicable and has beeninitially developed for use with webs of paper and, accordingly, will bedescribed with reference to this application.

Measurement of the speed or velocity of propagation of ultrasonic energyin paper sheets is well known as a nondestructive test for predictingthe mechanical strength of paper sheets and other structures constructedfrom paper sheets, see, for example, U.S. Pat. No. 4,574,634 which isincorporated herein by reference. Many manufacturers have replaced lesssophisticated destructive tests with such nondestructive tests androutinely perform the nondestructive ultrasonic energy tests on samplesof finished paper products. Unfortunately, as long as the ultrasonictests are performed off-line on finished paper products, substantialamounts of defective product may be produced before it has even beendetermined that the product is defective.

To correct this problem, on-line testing using ultrasonic energy hasbeen pursued. See, for example, U.S. Pat. Nos. 4,291,577 and 4,730,492which are incorporated herein by reference. These on-line testingarrangements utilize rotating wheels or drums having surface mountedtransducers which are rotated with a web of paper such that there iseffectively no relative motion between the transducers and the web beingtested. Two or three transducers are oriented on the drums or wheels tomake substantially simultaneous contact with the web of paper.

An impulse of ultrasonic energy is generated at a transmittingtransducer when the transducers are in contact with the web. The impulseis then detected at a second receiving transducer or second and thirdreceiving transducers. The velocity of the ultrasonic energy through theweb is then calculated using the arrival time (or arrival timedifference if three transducers are used) and the distance between thetransducers. Three transducers were provided in an attempt to removetiming errors introduced into the calculated velocities by phase shiftsin the electrical and mechanical interactions of the transducers.

Unfortunately, none of the ultrasonic energy on-line testingarrangements pursued to date has resulted in a practical commercialmeasurement for webs of paper or other materials as they are beingmanufactured. Accordingly, a need remains for an accurate and reliabletesting arrangement to determine mechanical properties of webs of sheetmaterial as the webs are being manufactured by measuring the propagationspeed of ultrasonic energy through the webs. Preferably such anarrangement would tolerate relative motion between ultrasonictransducers and webs of material being measured for association withconventional web scanning equipment.

SUMMARY OF THE INVENTION

This need is met by the methods and apparatus of the present inventionwherein the velocity or speed of ultrasonic energy in moving webs ofmaterial is measured on-line as the webs are manufactured by engagingand preferably scanning a measuring head over the web of material. Theadditional noise generated by relative motion between ultrasonictransducers in the measuring head and the web of material due to themotion of the web and/or scanning the head over the web can be overcomein accordance with the present invention to substantially simplify thetesting apparatus.

Improved ultrasonic energy transducers are employed wherein a materialcontacting member is secured to an interface region between oppositelyoperated first and second regions which intensify and amplify themovement of the interface region and hence the materialcontacting-member by operating in a push-pull mode relative to theinterface region. The transducers are calibrated by means of referencepaths having known ultrasonic transmission characteristics whichreference paths are separate and apart from the web of material which isbeing measured. The transducers can be selectively contacted with amoving web of material or not under the influence of vacuum which isapplied to the measuring head into which the transducers are installed.

The transducers are initially calibrated using an interconnectingreference path. A single transducer can be used to transmit ultrasonicenergy through a web with the resulting ultrasonic energy being receivedby one, two or more transducers to determine the velocity of one, two ormore modes of ultrasonic energy waves in the plane of the web. In anillustrated embodiment of the invention, the velocity of ultrasoniclongitudinal waves and ultrasonic shear waves are measured using a firsttransmitting transducer, a second receiving transducer and a thirdreceiving transducer. A fourth receiving transducer is illustrated andcan be used to receive combined ultrasonic longitudinal and shear waves,if desired, for example to provide redundancy.

An ultrasonic energy signal made up of a selected number of cycles of aselected frequency is transmitted to a transmitting transducer. A largeplurality of such ultrasonic energy signals are received by one or morereceiving transducers and digitally integrated or summed and averaged toeliminate the substantial noise which is present on the receivedultrasonic energy signals due to the relative motion of the transducersand the web of material being measured. The travel time between thetransmitting transducer and the receiving transducer or transducers isthen combined with the distance or distances therebetween to arrive atthe velocity or speed of the ultrasonic energy in a web being measured.

In accordance with one aspect of the invention, a transducer fortransmitting ultrasonic energy through sheet material and/or receivingultrasonic energy therefrom comprises piezoelectric means having atleast first and second portions which interface with one another at aninterface region for generating and/or receiving the ultrasonic energy.Material contact means couple the piezoelectric means to the sheetmaterial with the material contact means being secured to the interfaceregion of the piezoelectric means. Electrical contact means are providedfor making an electrical connection to the at least first and secondportions of the piezoelectric means.

The piezoelectric means may comprise a bar of piezoelectric material,approximately a first half of the bar defining the first portion of thepiezoelectric means and approximately a second half of the bar definingthe second portion of the piezoelectric means. The interface region ofthe piezoelectric means comprises a central portion of the bar extendingbetween the first and second portions. The electrical contact means maycomprise a first contact electrically connected to the first half of thebar and a second contact electrically connected to the second half ofthe bar. The electrical contact means preferably comprises an electrodefilm deposited on the bar with the electrode film being removed over theinterface region to separate and define the first and second contacts.To dampen extended ultrasonic oscillations beyond termination of anultrasonic driving signal, preferably a dimension of the materialcontact means between the piezoelectric means and the material is madeequal to approximately one quarter wavelength of the ultrasonic energy.

Alternately the piezoelectric means may comprise a disc of piezoelectricmaterial, approximately a first half of the disc defining the firstportion of the piezoelectric means and approximately a second half ofthe disc defining the second portion of the piezoelectric means. Theinterface region of the piezoelectric means comprises a diametricportion of the disc extending between the first and second portions withthe material contact means being secured to a central portion of theinterface region approximately at the center of the disc and extendingaxially therefrom.

For this embodiment, the electrical contact means comprises a firstcontact electrically connected to the first half of the disc and asecond contact electrically connected to the second half of the disc.The interface region may be defined by at least partially cuttingthrough the disc along the diametric portion of the disc. The interfaceregion is defined at least in part by cutting through a central part ofthe disc along the diametric portion thereof, the central part extendingbetween two opposite edges of an annular ring of the disc which annularring maintains the integrity of the disc. The first and second contactsare separate from the annular ring and the contact means may furthercomprise an annular contact substantially corresponding and electricallyconnected to the annular ring.

To further enhance movement of the interface region, the transducer mayfurther comprise support means for supporting the piezoelectric meansand for restraining movement of the at least first and second portionsof the piezoelectric means spaced from the interface region.

More than two portions may be defined for a transducer. For example, thepiezoelectric means may have at least first, second, third and fourthportions, the first and second portions being on opposite sides of theinterface portion and being linearly aligned with one another, and thethird and fourth portions being on opposite sides of the interfaceportion and being linearly aligned with one another, the first andsecond portions being angularly oriented relative to the third andfourth portions. For this embodiment, the electrical contact meansfurther provides for making electrical connection to the third andfourth portions. For a four portion transducer, preferably the first andsecond portions are oriented at a 90° angle relative to the third andfourth portions.

Alternately, the piezoelectric means may have first, second, third andfourth portions which interface with one another at the interfaceregion, the piezoelectric means comprising a disc of piezoelectricmaterial, approximately a first quarter of the disc defining the firstportion of the piezoelectric means and approximately a second quarter ofthe disc diametrically opposite to the first quarter defining the secondportion of the piezoelectric means, approximately a third quarter of thedisc defining the third portion of the piezoelectric means andapproximately a fourth quarter of the disc diametrically opposite to thethird quarter defining the fourth portion of the piezoelectric means.The interface region of the piezoelectric means comprises a centralportion of the disc extending between the first, second, third andfourth portions. The electrical contact means comprises a first contactelectrically connected to the first quarter of the disc, a secondcontact electrically connected to the second quarter of the disc, athird contact electrically connected to the third quarter of the disc,and a fourth contact electrically connected to the fourth quarter of thedisc.

Preferably, the contact means comprises an electrode film deposited onthe disc, the electrode film being removed over the interface region andbetween the first, second, third and fourth portions of thepiezoelectric means to separate and define the first, second, third andfourth contacts. The transducer may further comprise support means forsupporting the piezoelectric means and the material contact means. Forthis embodiment, the material contacting means comprises rod meansrigidly secured by the support means and extending through and a defineddistance beyond the piezoelectric means.

In accordance with another aspect of the present invention, apparatusfor on-line measurement of velocities of ultrasonic energy in sheetmaterial comprises a first transducer for transmitting ultrasonic energythrough the sheet material during manufacture of the sheet material anda second transducer for receiving ultrasonic energy from the sheetmaterial during manufacture of the sheet material. Housing meanssupports the first and second transducers in a defined orientationrelative to one another for engagement with the sheet material duringmanufacture. First reference path means are coupled between the firsttransducer and the second transducer for providing a reference pathhaving known ultrasonic energy transmission characteristics between thefirst and second transducers.

The apparatus may further comprise a third transducer for receivingultrasonic energy from the sheet material during manufacture of thesheet material, the housing means further providing for supporting thethird transducer in a defined orientation relative to the first andsecond transducers for engagement with the sheet material duringmanufacture thereof. Second reference path means are coupled between thefirst transducer and the third transducer for providing a reference pathhaving known ultrasonic energy transmission characteristics between thefirst and third transducers. The housing means comprises air bearingmeans for supporting the housing on the sheet material and engagementmeans for selectively engaging the first, second and third transducerswith the sheet material. The engagement means may comprise vacuumapplication means for drawing the sheet material to the first, secondand third transducers.

The apparatus preferably further comprises driver means for driving thefirst transmitter means to transmit a selectable number of cycles ofdefined frequency ultrasonic energy and receiver means for receivingsignals representative of the ultrasonic energy from the second andthird transducers and identifying the selectable number of cycles of thedefined frequency ultrasonic energy.

In accordance with yet another aspect of the present invention, a methodof on-line measurement of velocities of ultrasonic energy in sheetmaterial comprises the steps of: (a) providing a first transducer fortransmitting ultrasonic energy through sheet material as the sheetmaterial is being manufactured; (b) providing a second transducer forreceiving ultrasonic energy from the sheet material, the secondtransducer being positioned a known distance from the first transducer;(c) calibrating the first and second transducers via a reference pathcoupled therebetween to determine a time of origination of ultrasonicenergy transmitted through the sheet material by the first transducer,the reference path having known ultrasonic energy transmissioncharacteristics; (d) engaging the first and second transducers with thesheet material as it is being manufactured; (e) transmitting a selectednumber of cycles of defined frequency ultrasonic energy through thesheet material via the first transducer; (f) receiving the selectednumber of cycles of defined frequency ultrasonic energy from the sheetmaterial via the second transducer; (g) determining the time of receiptof an origination point of the selected number of cycles of definedfrequency ultrasonic energy; and, (h) determining the velocity of theultrasonic energy from the known distance of the second transducer fromthe first transducer and the origination point of the selected number ofcycles of defined frequency ultrasonic energy.

The step (c) of calibrating the first and second transducers via areference path coupled therebetween preferably comprises the steps of:(i) transmitting a selected number of cycles of defined frequencyultrasonic energy through said reference path via said first transducer;(j) receiving said selected number of cycles of defined frequencyultrasonic energy from said reference path via said second transducer;and, (k) determining the time of receipt of an origination point of saidselected number of cycles of defined frequency ultrasonic energy.

It is thus an object of the present invention to provide improvedmethods and apparatus for on-line measurement of the velocity or speedof ultrasonic energy in webs of material as the webs are beingmanufactured; to provide improved methods and apparatus for on-linemeasurement of the velocity or speed of ultrasonic energy in webs ofmaterial as the webs are being manufactured wherein improved ultrasonicenergy transducers are employed; to provide improved methods andapparatus for on-line measurement of the velocity or speed of ultrasonicenergy in webs of material as the webs are being manufactured whereintransducers are calibrated by means of one or more reference paths whichare separate and apart from the webs of material which are beingmeasured; and, to provide improved methods and apparatus for on-linemeasurement of the velocity or speed of ultrasonic energy in webs ofmaterial as the webs are being manufactured wherein noise due torelative movement between webs of material and ultrasonic transducers issubstantially eliminated by collecting a large number of samples anddigitally integrating those samples.

Other objects and advantages of the invention will be apparent from thefollowing description, the accompanying drawings and the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a first embodiment of an improvedultrasonic transducer of the present invention;

FIG. 1E is an exploded view of the transducer of FIG. 1;

FIG. 2 is a cross sectional view of the transducer of FIG. 1additionally showing a transducer support housing;

FIG. 3 is a perspective view of a second embodiment of an improvedultrasonic transducer of the present invention having a circularpiezoelectric element, see drawing sheet 2;

FIG. 3E is an exploded view of the transducer of FIG. 3;

FIG. 4 is a cross sectional view of the transducer of FIG. 3;

FIG. 5 is a perspective view of a third embodiment of an improvedultrasonic transducer of the present invention;

FIG. 5E is an exploded view of the transducer of FIG. 5;

FIG. 6 is a cross sectional view of the transducer of FIG. 5;

FIG. 7 is a perspective view of a fourth embodiment of an improvedultrasonic transducer of the present invention having a circularpiezoelectric element, see drawing sheet 2;

FIG. 7E is an exploded view of the transducer of FIG. 7;

FIG. 8 is a cross sectional view of the transducer of FIG. 7;

FIG. 9 is a schematic view of a piezoelectric element illustratingoperation of a transducer in accordance with the present invention;

FIG. 10 is a series of graphs representing electrical drive signals forthe piezoelectric element of FIG. 9 and the resulting motion of aninterface portion;

FIG. 11 is a schematic plan view of a fifth embodiment of an improvedultrasonic transducer of the present invention;

FIG. 12 is a bottom view of a measuring head for performing ultrasonicmeasurements on moving webs of material in accordance with the presentinvention;

FIG. 13 is a sectional view taken along the section line 13--13 of FIG.12;

FIG. 14 is a perspective view of a conventional measuring or gaugingsystem into which the present invention is preferably incorporated forperforming ultrasonic measurements on moving webs of material as theyare being manufactured, see drawing sheet 3;

FIG. 15 is a schematic block diagram of an on-line ultrasonic velocitymeasuring system operable in accordance with the present invention tomeasure a web as it is being manufactured;

FIG. 16 is graph of an output signal for a single multiple cycleultrasonic energy wave generated by a transducer used as a receiver foron-line measurement of a web of material;

FIG. 17 is an integration of a relatively large number of output signalsas shown in FIG. 16 with the noise substantially removed by theintegration operation;

FIG. 18 is a schematic graphic representation illustrating operation ofan on-line ultrasonic velocity measurement system for webs of materialduring manufacture; and

FIG. 19 is a graph of a digitally integrated series of receivedultrasonic energy signals illustrating determination of average delaytime of the signals through a web of material from which the velocity ofthe ultrasonic energy in the web is determined.

DETAILED DESCRIPTION OF THE INVENTION

In previous attempts at performing on-line testing of webs of materialusing ultrasonic energy, transducers were placed on the periphery ofwheels or drums. The wheels or drums were then engaged with and rotatedon the moving web of material such that the transducers periodicallycontacted the web and did not move substantially relative to the webduring contact. Ultrasonic measurements were made during the time thatboth transmitting and receiving transducers were simultaneously incontact with the web.

Taking ultrasonic measurements at approximately zero relative velocitybetween the transducers and a web being measured substantially reducesmechanical noise which is otherwise produced by moving the transducersrelative to the web. However, rotating wheels or drums substantiallyincrease the complexity of measuring apparatus as is apparent from thelater two of the above referenced patents. Further, it is very difficultif not impossible to incorporate such rotating measurement systems intoa conventional web scanner which is routinely used to measure othercharacteristics of webs of material as they are being manufactured, forexample basis weight in the case of paper webs.

In spite of reduced noise levels due to synchronous rotation oftransducers with a web to be measured and low noise optical signalcoupling to the transducers, known ultrasonic web measurement systemshave been unable to provide reliable on-line measurements of webprocesses. In part the problems encountered in utilizing theseultrasonic measurement systems were due to low ultrasonic signal levelsassociated with the transducers used to transmit ultrasonic energy tothe web and receive ultrasonic energy from the web. In addition,variables inherent in the transducers and the interfaces of thetransducers to the web were not properly compensated in the knownmeasurement systems.

In an attempt to correct errors in measurements made with systems usingtwo transducers, a third transducer was added. For measurements madeusing three transducers, one transducer transmitted ultrasonic energywhile the second and third transducers received the ultrasonic energyafter traveling through a web whose characteristics were to be measured.The second and third receiving transducers were positioned at differentdistances from the first transmitting transducer. The travel time fromthe first transmitting transducer to the second and third receivingtransducers was used to calculate travel time of the acoustic energy inthe web. The electrical delays in the circuitry and electro-acousticdelays in the transducers were to be compensated by subtracting thepropagation time to the nearer of the receiving transducers from thepropagation time to the farther of the receiving transducers.

While this approach appears correct, it does not account for differencesin the transducers, which can be significant even for identicallyprepared transducers, or differences in the interfaces between theindividual transducers and the web. Transducer differences andtransducer interfaces also vary over time and in response to theirenvironment and these variations are not uniform from transducer totransducer. Further, the path traveled to the second and third receivingtransducers are not identical to one another. Accordingly, even if thetransducers and transducer/web interfaces are identical, the effectiveelectro-acoustic delays in the transducers could not be eliminated bysubtracting the travel time of the acoustic energy to the nearer of thereceiving transducers from the travel time to the farther of thereceiving transducers.

Applicants have recognized that the transducers and associatedelectronics need to be calibrated over an ultrasonic path having knowncharacteristics rather than through the web which is being measured. Toperform this calibration, a reference path is interconnected between atransmitting transducer and each of one or more receiving transducers.The transducers can then be calibrated to compensate for differingcharacteristics of the transducers.

To further improve accuracy for the on-line measurement methods andapparatus of the present invention, a selected number of cycles of theultrasonic energy is transmitted by the transmitting transducer suchthat the frequency and number of cycles can be used to assist inverifying the presence of transmitted ultrasonic energy at the receivingtransducers and the point in time of the origin or onset of receipt ofthat ultrasonic energy. The beginning point in time of the transmittedultrasonic energy is determined by identifying the frequency and numberof cycles of ultrasonic energy received by a receiving transducer over acalibration reference path, with calibration being periodicallyperformed. The beginning point of the received ultrasonic energy astransmitted in-plane through the web of material to be measured is thendetermined by identifying the frequency and number of cycles of theultrasonic energy received by the receiving transducer.

The travel time can then be accurately determined within limitsdetermined by variations in the interfaces between the transducers andthe web. The transmission of a selected number of cycles of knownfrequency ultrasonic energy signals permits analysis of ultrasonicenergy signals received by a transducer. Discrepancies between thereceived ultrasonic energy signals and the known transmitted signalsalert the system to changes which can be induced by variations in theinterfaces between the transducers and the web or by external noise. Ifthe discrepancies are sufficiently large, a received signal is rejectedas being corrupt. Discrepancies in acceptably received ultrasonic energysignals are suggestive of corrections which can be made to furtherimprove accuracy of measurements made in accordance with the invention.Knowing the travel time and the distance between the transmittingtransducer and the receiving transducer or transducers, thecorresponding velocity or velocities of the ultrasonic energy can bedetermined readily.

By utilizing improved transducers and operating the transducers inaccordance with the methods of the present invention, accuratemeasurements of the velocity of ultrasonic energy in moving webs ofmaterial can be determined as the webs are being manufactured withoutrequiring the complicated and cumbersome rotating wheels or drums ofpreviously proposed on-line measuring systems. The improved transducersare incorporated into a measuring head which is supported upon andseparated from the moving web of material by compressed air which isejected through air bearing surfaces of the measuring head.

The transducers which are contained within the head selectively engagethe web as it passes over the measuring head under the control of vacuumwhich is applied for contact and released for noncontact. It ispresently preferred to bring all transducers into contact with the webor to remove all transducers from contact with the web; accordingly,selective contact as used herein is for all transducers. However, insome applications it may be preferred to bring only two transducers intocontact with the web at one time. If contact is limited to twotransducers at a time, the possibility of reflections from onetransducer interfering with the receipt of ultrasonic energy signals byanother transducer is eliminated or reduced.

A single measuring head can be moved across a moving web of material tomeasure characteristics of the web or a series of measuring heads can beprovided across a web. Since the measuring head can be moved across amoving web of material while performing measurements, a singlemeasurement head can be incorporated into or otherwise associated with aconventional web scanner which is routinely used to measure othercharacteristics of webs of material as they are being manufactured, forexample the basis weight of paper webs.

Improved transducers for transmitting and/or receiving ultrasonic energywill now be described with reference to FIGS. 1-8. The first embodiment100 and third embodiment 102 of FIGS. 1 and 5 are constructed using agenerally rectangular bar of piezoelectric material such as PZT (leadzirconate titanate); and, the second embodiment 104 and fourthembodiment 106 are constructed of a generally circular disc ofpiezoelectric material. Improved transducers in accordance with thepresent invention utilize piezoelectric means for generating and/orreceiving ultrasonic energy. In the later described applications of theillustrated transducer embodiments, each transducer serves as either atransmitter or a receiver; however, it is possible to utilize a singletransducer as both a transmitter and a receiver in accordance with thepresent invention.

The piezoelectric means of all of the illustrated embodiments operate ina similar manner. Accordingly, for ease of illustration and description,the operation of the piezoelectric means will be described withreference to the embodiment of FIG. 1. Once understood, the operation ofmultiple pairs of portions of piezoelectric material will be apparent,and two pairs will be described with reference to the embodiments ofFIGS. 3-4 and 7-8.

As shown in FIGS. 1 and 1E, a generally rectangular bar 108 ofpiezoelectric material is entirely polarized in one direction, forexample as shown by the arrows 110. The bar 108 has a first portion 108aand a second portion 108b which interface one another at an interfaceregion 108c. Electrical contact means comprising electrical contacts112, 114 are provided for making an electrical connection to the lowersurfaces of the first and second portions 108a, 108b of the bar 108 ofpiezoelectric material. It is noted that different polarizations can beused for the first and second portions 108a, 108b provided drive signalsand signal handling procedures are appropriately adapted.

In the illustrated embodiment, the contact means also includes anelectrical contact 116 on the upper surface of the bar 108. To reducenoise, the contact 116 is preferably connected to ground potential;however, it can be allowed to float if desired. The contacts 112, 114,116 are preferably formed by depositing an electrode film on thecorresponding surfaces of the bar 108. The contacts 112, 114 can beformed from a single deposition by removing the electrode film over thetransducer portion 108c of the bar 108.

Material contacting means comprising a cylindrical stud 118 in theembodiment of FIGS. 1-4, provides for coupling the bar 108 ofpiezoelectric material to a web of sheet material, the characteristicsof which are to be measured. The stud 118 is secured to the interfaceregion 108c of the bar 108 by means of a threaded extension 120 and anut 122 as shown in FIGS. 1E and 2.

To transmit ultrasonic energy through a web of material, the top 118a ofthe stud 118 is placed in contact with a web of material to be measuredand the contacts 112, 114 are driven with oppositely phased signals A,-A such that as the signal on the contact 112 is increasing the signalon the contact 114 is decreasing and vice versa as shown in FIGS. 9 and10. When a portion of the bar 108 of piezoelectric material is driven bya negative signal, it expands with the volume remaining constant.Conversely, when a portion of the bar 108 is driven by a positivesignal, it contracts with the volume remaining constant.

Accordingly, as the oppositely phased signals A, -A drive the first andsecond portions 108a, 108b of the bar 108 of piezoelectric material, theinterface portion 108c is pushed by one portion and pulled by the otherto intensify and expand the motion of the interface portion 108c andconsequently the motion M of the stud 118 which is secured to theinterface portion 108c. As shown in FIG. 2, the transducer 100 mayfurther comprise support means S for supporting the bar 108. The motionM of the interface portion 108c and hence the stud 118 may be furtherenhanced by thus supporting the bar 108 and thereby restraining movementof the ends of the bar 108.

A bar 108 of piezoelectric material is also used in the third embodimentof FIGS. 5-6. For ease of description and identification, elements ofthe third embodiment which are the same as or have correspondingelements in the first embodiment will be identified by the sameidentifying numerals. In this embodiment, the material contacting meanscomprises rod means for levered amplification of the motion of the bar108. This embodiment includes a generally rectangular base meanscomprising a brass block 124 as illustrated for supporting the bar 108of piezoelectric material and the rod means.

The rod means comprises a section of stainless steel dowel 126 with thetop 126a of the dowel 126 being placed in contact with a web of materialto be measured. The dowel 126 is secured in a receiving opening 124a ofthe block 124 and the bar 108 is secured to the block 124 by means of alayer 128 of epoxy or other appropriate adhesive or securing means. Thedowel 126 thus serves as a lever with the bar 108 of piezoelectricmaterial serving as a moving fulcrum to multiply the motion of the top126a of the dowel 126.

The push-pull operation which amplifies the motion of the interfaceregion of the piezoelectric bar 108 or other two portion configurationof piezoelectric material when operating as a transmitter also improvesthe performance of a transducer when operated as an ultrasonic receiver.Signals generated by the piezoelectric material are received from thecontacts 112, 114, and preferably differentially processed. If an axialforce, a force in the z-direction as shown in FIG. 1, is applied to thestud 118 or the dowel 126, approximately the same level of signal isgenerated on each of the contacts 112, 114 such that there is nodifferential signal generated. Also, approximately the same level ofsignal is generated on the contacts 112, 114 for forces applied in thex-direction.

However, for forces applied in the y-direction or in alignment with thebar 108 or two portions of piezoelectric material, a differential signalis generated across the contacts 112, 114. The generation of adifferential signal on the contacts 112, 114 can be best understood bynoting that a force in the y-direction tends to place one portion of thebar 108 of piezoelectric material into compression and the other portioninto expansion. Thus, when used as a differential receiver, thetransducers of the present invention are selective in terms of thedirection of the applied forces to which they best respond therebyreducing unwanted signals otherwise generated and possibly interferingwith accurate measurements.

It should be apparent that the first and third embodiments share commonpiezoelectric elements as do the second and fourth embodiments, whilethe first and second embodiments share common material contact means asdo the third and fourth embodiments. Accordingly, common elements of thefour transducer embodiments will be identified using the same numeralsfor ease of description and identification. Corresponding elements whichare generally circular or disc shaped as opposed to being generally barshaped will be identified by the same numeral with a prime (') todistinguish the two. The second embodiment 104 of FIGS. 3-4 and thefourth embodiment 106 of FIGS. 7-8 comprise a disc 130 of piezoelectricmaterial.

Each piezoelectric disc 130 comprises first and second portions 132, 134and third and fourth portions 136, 138. Separate electrical connectionsare made to the first, second, third and fourth portions 132-138 bymeans of electrical contact means comprising first, second, third andfourth contacts 132'-138' which substantially cover the lower surfacesof the first, second, third and fourth portions 132-138. The first,second, third and fourth contacts 132'-138' preferably are formed bydepositing an electrode film and then removing the film to definesectors which in turn define the first, second, third and fourthcontacts 132'-138'. The interface portion of each piezoelectric disc 130is the central portion of the disc 130 and the material contacting meansis secured to the interface portion in the same manner as describedabove relative to the first and third embodiments of FIGS. 1-2 and 5-6as should be apparent from FIGS. 3-4 and 7-8.

To enhance movement of the first and second portions 132, 134 and thethird and fourth portions 136, 138, preferably they are defined bypartially cutting through the disc 130 along diametric sections of thedisc 130 which separate the portions from one another. As shown in FIGS.4 and 8, the cuts 130a are through a central part of each disc 130 andextend between an annular ring 130b which maintains the integrity ofeach disc 130. The cuts can be made by plunge cutting using a circularsaw as suggested by the arcuate ends of the cuts 130a.

If an electrode film is used to define the contacts 132'-138' on thelower surface of each disc 130, then the remainder of each diametricsection is defined by removing the film which otherwise covers theannular ring 130b. If desired and as illustrated in FIG. 8, the lowersurface of the annular ring 130b may be covered by a separate electrode130c formed from an electrode film or otherwise and connected to groundto reduce noise within the system.

The first and second portions 132, 134 operate as previously describedwith reference to the bar 108 of FIG. 1 to transmit ultrasonic energythrough a web of material and/or to receive ultrasonic energy from a webof material. Electrical activation of the first and second portions 132,134, causes motion of the material contact means along a diameter 140which generally bisects the sectors or portions 132, 134, see FIGS. 3,3E, 7 and 7E. This motion generates substantially pure longitudinalwaves in alignment with the diameter 140 and substantially pure shearwaves perpendicular thereto, with proportional mixtures of longitudinaland shear waves in directions therebetween. Differential signals arealso generated on the contacts 132', 134' of the first and secondportions 132, 134 for ultrasonic energy inducing motion of the materialcontact means along the diameter 140.

In a similar manner, electrical activation of the third and fourthportions 136, 138, causes motion of the material contact means along adiameter 142 which generally bisects the sectors or portions 136, 138,see FIGS. 3 and 7. This motion generates substantially pure longitudinalwaves in alignment with the diameter 142 and substantially pure shearwaves perpendicular thereto with proportional mixtures of longitudinaland shear waves in directions therebetween. Differential signals arealso generated on the contacts 136', 138' of the first and secondportions 136, 138 for ultrasonic energy inducing motion of the materialcontact means along the diameter 142.

It should be apparent that the disc 130 can be divided into more thantwo pairs of opposite segments or portions if substantially purelongitudinal and/or shear ultrasonic energy waves are to be coupledthrough a web of material and/or received from a web of material in morethan the two directions generally defined by the diameters 140, 142. Seefor example, FIG. 11 wherein three pairs of sectors or portions aredefined on a piezoelectric disc 130. In addition, the form and directionof ultrasonic energy waves can be varied electrically by phase changesof the signals used to drive the transducers. In this way, longitudinaland/or shear energy waves can be transmitted in substantially anydirection using transducers having piezoelectric elements having onlytwo portions. Such configurations and/or operations may be preferred insome applications to reduce the number or complexity of transducers.

Further, while the transducers have been described as being constructedof a single bar or disc of piezoelectric material, each transducer canbe constructed from two or more piezoelectric elements. Thus, each ofthe portions of a bar or sectors of a disc can be separate piezoelectricelements or constructed themselves from a combination of piezoelectricelements. It is also preferred to make the piezoelectric elements of thetransducers, however constructed, resonant at approximately thefrequency of the ultrasonic energy being handled by the transducers.This can be accomplished by making the long dimension of the bar 108 orthe diameter of the disc 130 equal approximately to one wavelength, λ,of the ultrasonic energy.

Having thus described illustrative embodiments of improved ultrasonicenergy transducers of the present invention, methods and apparatus formeasuring the speed or velocity of ultrasonic energy in a moving web ofmaterial utilizing the transducers will now be described. For suchmeasurement operations, one or more ultrasonic transducers are contactedwith a moving web of material. In one illustrative embodiment,ultrasonic transducers are incorporated into a measuring head 150 asshown in FIGS. 12 and 13.

One measuring head 150 or a plurality of measuring heads such as themeasuring head 150 may be used at one or a plurality of locations acrossa web of material for measuring the speed or velocity of ultrasonicenergy in a moving web and inferring strength characteristics of the webfrom the velocity measurements. However, it is currently preferred toincorporate the measuring head 150 into a sensor 152 or associate themeasuring head 150 with the sensor 152. In this way, the measuring head150 is scanned across a moving web 154 of material in conventional webscanning operations routinely used to measure characteristics of the web154 of material as it is being manufactured, for example the basisweight of a paper web. See the arrangement illustrated in FIG. 14.

The illustrated measuring head 150 includes four cavities 156, 158, 160,162 in its bottom or web engaging face. As illustrated, four transducers164, 166, 168, 170 constructed in accordance with the third embodimentof FIGS. 5-6, are inserted into the cavities 156-162, respectively. Thetransducers 164-170 are sized and supported such that the materialcontacting means or dowels 126 are slightly recessed below the bottomface of the measuring head 150. The measuring head 150 includes a seriesof air passages 172 which terminate in air bearing openings 174 aroundthe bottom face of the head 150 shown in FIG. 12.

As shown in FIG. 13, a web 176 of material moving past the head 150 issupported a distance from the bottom face of the head 150 by air flowingfrom the air bearing openings 174 therein. The web 176 can beselectively engaged with the transducers 164-170 or not dependent uponthe application of vacuum to the cavities 156-162. Vacuum is applied tothe cavities 156-162 or released by means of vacuum ports 178 formedinto angularly inclined upper wall sections 180 of the cavities 156-162,see FIG. 12.

The transducers 164-170 are supported upon acoustic isolation pads 182and the cavities 156-162 are filled to a level spaced from the bottomface of the measuring head 150 with a sound absorbing potting compound184. In the illustrated embodiment, the transducer 164 is set up totransmit ultrasonic energy through the web 176, or the web 154 of FIG.14, and the transducers 166, 168, 170 are set up to receive ultrasonicenergy from the web 176, or the web 154.

To compensate for electro-acoustic characteristics of the transducers164-170, reference paths 186, 188, 190 are extended between the acousticenergy transmitting transducer 164 and the acoustic energy receivingtransducers 166, 168, 170. In the illustrated embodiment of FIGS. 12 and13, the reference paths 186, 188, 190 comprise quartz strands which aresecured to the transducers 164-170 by means of an appropriate adhesivesuch as epoxy or otherwise. Of course other ultrasonic transmittingmaterials can be used to define the reference paths as will be apparentto those skilled in the art. An ultrasonic signal is then transmittedover the reference paths 186-190 to calibrate the transducers 164-170.The beginning point in time of transmitted ultrasonic energy isaccurately identified by means of periodic calibration over a referencepath. For example, for a measuring system wherein the measuring head isscanned across the web 154 of material being manufactured as generallyshown in FIG. 14, the calibration may be performed once each scan. Ofcourse, calibration can be performed more or less frequently as requiredfor accurate web measurement.

While four transducers 164-170 are shown in the embodiment of themeasuring head 150 of FIG. 12, it is currently preferred to utilize onlythree transducers in a web measuring system operable in accordance withthe present invention. As shown schematically in FIG. 15, a firsttransducer 192 transmits ultrasonic energy through a web 194 of sheetmaterial as it is being manufacturing and therefore is traveling in thedirection of an arrow 196.

The transmitting transducer 192 is constructed in accordance with theforegoing teachings and description made relative to FIGS. 1-10. Asignal generator 198 drives the transmitter 192 in response toactivation signals received from a processor 200. When in contact withthe web 194, the transducer 192 transmits a selectable number of cyclesof ultrasonic energy through the web 194, four cycles currently beingpreferred. The frequency of the ultrasonic energy is selectable betweenapproximately 40 kilohertz and 100 kilohertz with 60 kilohertz currentlybeing preferred in view of resolution and size required for the system.The power P level of the drive signal produced by the signal generator198, the number # of cycles of the signal and the frequency F can beselected by the processor 200. Alternately, as shown by dotted lineinputs to the signal generator 198, these selections can be made bydirect inputs.

In response to the drive signal generated by the signal generator 198the first transducer 192 generates substantially pure longitudinalenergy waves 202 in the direction of a second transducer 204 andsubstantially pure shear energy waves 206 in the direction of a thirdtransducer 208. The second and third transducers 204, 208 areconstructed in accordance with the foregoing teachings and descriptionmade relative to FIGS. 1-10. The second transducer 204 is oriented torespond to the longitudinal energy waves 202 and the third transducer208 is oriented to respond to the shear energy waves 206. Thetransducers 192, 204, 208 are supported in a housing 150', such as thehousing 150 as previously described, to accomplish the notedtransmission and reception of ultrasonic energy waves.

Reference path means, comprising in the illustrated embodiment a quartzstrand 210 and a quartz strand 212, are coupled between the firsttransducer 192 and the second and third transducers 204, 208,respectively, for defining reference paths having known ultrasonicenergy transmission characteristics therebetween.

As the energy waves are received by the transducers 204, 208,differential signals are generated by the transducers 204, 208 andpassed to signal conditioning circuitry 214, 216. The resulting outputsignals from the signal conditioning circuitry 214, 216 are passed toanalog-to-digital (A/D) converters 218, 220. The A/D converters 218, 220digitize the output signals from the signal conditioning circuitry 214,216 and passed the resulting digital signals to the processor 200 wherethey are processed to determine the speed or velocity of ultrasonicenergy in the web 194 of material.

It is possible and may reduce the circuitry and tolerances required ofcircuitry operation to multiplex the signals received from thetransducers 204, 208. For a multiplex arrangement, all such signals areprocessed by one channel such that any discrepancies between two signalprocessing channels are eliminated. Multiplexed operation and itsadvantages are well known in the art and will not be described furtherherein.

Since the ultrasonic energy measurements are being taken as thetransducers 192, 204 and 208 are in contact with and moving in both themachine direction and cross direction, if scanned, relative to the web194 of material, substantial noise results in output signals generatedby the receivers 204, 208. The resulting noise is apparent in an outputsignal 222 generated by either the transducer 204 or the transducer 208for a single received multiple cycle ultrasonic energy signal as shownin FIG. 16. The output signal 222 is the result of sampling the outputsignal of a transducer receiving a 60 kilohertz ultrasonic energy signalat a 5 megahertz sample rate with approximately 500 samples being shownin FIG. 16.

To extract the received ultrasonic energy waveform from the noiseladened samples making up the output signal 222 of FIG. 16, a largenumber of samples are taken and synchronously, digitally integrated,i.e. a large number of samples are summed and averaged. By integratingor summing and averaging a large number of individual samples making upa corresponding number of output signals 222, for example 250 to 500,the randomly distributed noise generated by scanning the transducers192, 204, 208 and by the web sliding at manufacturing velocity acrossthe transducers 192, 204, 208, is substantially reduced resulting in acleaned output signal 224 as shown in FIG. 17.

The operation of an on-line measuring system for measuring velocities ofultrasonic energy in webs of material as the webs are being manufacturedwill now be described with reference to the drawing figures and, inparticular, FIGS. 14, 15, 18 and 19. The description will be for asingle transmitting transducer, the transducer 192, and a singlereceiving transducer, the transducer 204, for ease of description.However, expansion to two or more receiving transducers as well asvariations of the control of the transmitting transducer will beapparent from this two transducer illustrative description.

A web manufacturing operation is in progress and the sensor 152 of ascanner system is being scanned back and forth across the web, such asthe web 194, in the cross machine direction with the web moving in themachine direction. An on-line ultrasonic velocity measurement system inaccordance with the present invention has been associated with thesensor 152, for example as shown in FIG. 14 by incorporation into thesensor 152.

Initially vacuum is turned off to the measuring head 150' such that thehead 150' and transducers 192, 204 contained within the head 150' areseparated from the web 194 by an air bearing as previously described. Asshown in FIG. 19, a trigger pulse 226 is generated by the processor 200to activate the signal generator 198 to generate an ultrasonic energysignal comprising a selected number of cycles of a selected frequencyultrasonic energy, for example, four cycles of 60 kilohertz ultrasonicenergy. In response to the trigger pulse 226, the ultrasonic energysignal is passed to the transducer 192.

Because of the electro-acoustic characteristics of the transmittingtransducer 192, the ultrasonic energy signal does not instantaneouslyappear at the mechanical output of the transducer 192 but is delayeddependent upon the unique characteristics of the transducer 192.However, at some point in time 0, the ultrasonic energy signaloriginates at the mechanical output of the transducer 192.

Since vacuum is not being applied to the head 150', the transducer 192is not in contact with the web 194 and accordingly, no ultrasonic energyis transmitted through the web 194 by the transmitting transducer 192.However, the quartz strand 210 defines a reference path of knownultrasonic transmission characteristics between the transmittingtransducer 192 and the receiving transducer 204. In this way, acalibration ultrasonic energy signal is transmitted to the receivingtransducer 208 and received as an ultrasonic energy signal 228 shownideally in FIG. 18.

Because of the electro-acoustic characteristics of the receivingtransducer 204, the ultrasonic energy signal does not instantaneouslyappear at the electrical output of the transducer 204 but is delayeddependent upon the unique characteristics of the transducer 204.However, at some point in time t_(r) the ultrasonic energy signaloriginates at the electrical output of the transducer 204.

Since the effective ultrasonic energy signal 228 is not a pure sine waveas shown in FIG. 18, its point of origin or the point in time t_(r) isnot entirely clear from the resulting signal. However, by knowing thefrequency and number of cycles of ultrasonic energy which weretransmitted, the processor 200 is able to determine the point in timet_(r).

The determination of the point in time t_(r) of the effective receivedultrasonic energy signal can be performed by simply taking the datapoint which is closest to a baseline 232 of the signal. The point intime t_(r) can also be determined by interpolating between a data pointimmediately above the baseline 232 and a data point immediately belowthe baseline 232. A least squares regression of points surrounding thepoint in time t_(r) can also be used. These as well as otheralternatives for determining the point in time t_(r) of the effectivereceived ultrasonic energy signal will be apparent to those skilled inthe art.

Since the reference path has known ultrasonic energy transmissioncharacteristics, the 0 time point of origin of the ultrasonic energysignal can be determined from the ultrasonic energy signal 228 receivedby the transducer 204 since it precedes the origin of the ultrasonicenergy signal at the receiving transducer 204 by a determinable timet_(RP).

The reference path is preferably made longer than the measurement paththrough the web of material such that the ultrasonic energy signaltransmitted through the reference path does not interfere withultrasonic velocity measurements of the web. The ultrasonic energysignal transmitted through the web does not interfere with thecalibration signal since the transmitting transducer 192 and thereceiving transducer 204 are not in contact with the web duringcalibration.

The ultrasonic energy signals do not immediately terminate upontermination of the ultrasonic energy signal generated by the signalgenerator 198. Accordingly, time must be allowed for the ultrasonicenergy signals in the web and the reference path to dissipate or dieaway before another ultrasonic energy signal is produced. To assist intermination of the signals, the stud 118 and the extension of the dowel126 between the piezoelectric element and its distal end 126a arepreferably made equal to approximately one quarter of the wavelength ofthe ultrasonic energy signal, 1/4λ. Termination of the ultrasonic energysignals is also assisted by making the long axis of the block 124 andthe diameter of the disc 124' equal to approximately one wavelength ofthe ultrasonic energy signal, λ, which is preferred. Other dampingarrangements, such as a lossy piezoelectric mounting or the like can beused in the present invention as will be apparent to those skilled inthe art.

Once the origin point in time 0 has been determined via calibrationthrough the reference path defined by the quartz strand 210 of FIG. 15,ultrasonic velocity measurements through the web 194 are performed. Itis noted that by using a reference path, such as the quartz strand 210,the unique characteristic of both the transmitting transducer 192 andthe receiving transducer 204 are used to determine the origin point intime 0. It should be apparent that a reference path could be defined bysimply touching the transmitting transducer 192 to the receivingtransducer 204 if that were possible in a given application. Of course,with the transducers fixed in the measuring head 150' a separate anddistinct reference path such as the quartz strand 210 must be provided.

To measure the velocity of ultrasonic energy through the web 194, vacuumis applied to the measuring head 150' such that the transducers 192, 204are drawn into contact with the web 194 with the remainder of the webengaging face of the head 150' being borne by air as shown in FIG. 13.Ultrasonic energy signals are once again triggered by the processor 200,transmitted by the transducer 192, but now received by the transducer204 after traveling through the web 194 of material which is beingmeasured. A large plurality of ultrasonic energy signals are received bythe transducer 204 and digitally integrated as previously described toresult in an effective ultrasonic energy signal 230 as shown ideally inFIG. 18 and more accurately in FIG. 19. Due to the differences in thescanning speed of the sensor 152 and the speed of the web 194, theplurality of measurements are at substantially the same location acrossthe web; however, the measurements extend over a length of web typicallyof one or two meters. This creates no problem since the webcharacteristics will normally be very consistent over such small lengthsof the web in the machine direction.

Since the effective ultrasonic energy signal 230 is not a pure sine waveas shown in FIG. 18 but an increasing magnitude wave as shown in FIG.19, its point of origin t_(o) is not entirely clear from the resultingsignal. However, by knowing the frequency and number of cycles ofultrasonic energy which were transmitted, the processor 200 is able todetermine a sufficiently accurate point of origin t_(o).

The determination of the point of origin t_(o) of the effective receivedultrasonic energy signal can be performed by simply taking the datapoint which is closest to the baseline 232 of the signal. The point oforigin t_(o) can also be determined by interpolating between a datapoint immediately above the baseline 232 and a data point immediatelybelow the baseline 232. A least squares regression of points surroundingthe point of origin t_(o) can also be used. These as well as otheralternatives for determining the point of origin t_(o) of the effectivereceived ultrasonic energy signal will be apparent to those skilled inthe art.

In any event, once the point of origin t_(o) is determined, the delaytime through the sheet t_(d) can be determined by relation to the originpoint in time 0 at which the ultrasonic energy signal originated. Usingthe delay time through the sheet t_(d) and the distance between thetransmitting transducer 192 and the receiving transducer 204, theprocessor is able to determine the velocity of the ultrasonic energythrough the web 194. The determined velocity is used in a well knownmanner to determine characteristics of the web 194 of sheet material.The characteristics so determined can be recorded, used to control themanufacturing process producing the web 194 and/or displayed to anoperator of the process.

The described operation of a system for measuring the velocity ofultrasonic energy in a web of material as it is being measured is highlyaccurate. However, some degree of error is introduced due to variationsin the interface of individual transducers to the web 194 of materialwhich is being measured. While it is not necessary for the highlyreliable and accurate measurement of the velocity of ultrasonic energyin a moving web of material as it is being manufactured, it is believedthat such errors can be corrected by empirical adjustments of themeasurement results dependent upon the characteristics of the interface.For example, it is believed that correction tables or factors can bedeveloped for different grades of paper to further improve the accuracyof measurements made using the present invention.

Having thus described the methods and apparatus of the present inventionin detail and by reference to preferred embodiments thereof, it will beapparent that modifications and variations are possible withoutdeparting from the scope of the invention defined in the appendedclaims.

What is claimed is:
 1. An ultrasonic energy transducer for contact withsheet material, said transducer comprising:a piezoelectric elementhaving at least first and second portions which interface with oneanother at an interface region; a material contact for coupling saidpiezoelectric element to said sheet material, said material contactbeing secured to said interface region of said piezoelectric element;and electrical contacts for making an electrical connection to said atleast first and second portions of said piezoelectric element.
 2. Anultrasonic energy transducer as claimed in claim 1 wherein saidpiezoelectric element comprises a bar of piezoelectric material,approximately a first half of said bar defining said first portion ofsaid piezoelectric element and approximately a second half of said bardefining said second portion of said piezoelectric element, saidinterface region of said piezoelectric element comprising a centralportion of said bar extending between said first and second portions;and, said electrical contacts comprising a first contact electricallyconnected to said first half of said bar and a second contactelectrically connected to said second half of said bar.
 3. An ultrasonicenergy transducer as claimed in claim 2 wherein said electrical contactscomprise an electrode film deposited on said bar, said electrode filmbeing removed over said interface region to separate and define saidfirst and second contacts.
 4. An ultrasonic energy transducer as claimedin claim 1 wherein a dimension of said material contact between saidpiezoelectric element and said sheet material equals approximately onequarter wavelength of said ultrasonic energy.
 5. An ultrasonic energytransducer as claimed in claim 1 wherein said piezoelectric elementcomprises a disc of piezoelectric material, approximately a first halfof said disc defining said first portion of said piezoelectric elementand approximately a second half of said disc defining said secondportion of said piezoelectric element, said interface region of saidpiezoelectric element comprising a diametric portion of said discextending between said first and second portions, said material contactbeing secured to a central portion of said interface regionapproximately at the center of said disc and extending axiallytherefrom; and, said electrical contacts comprising a first contactelectrically connected to said first half of said disc and a secondcontact electrically connected to said second half of said disc.
 6. Anultrasonic energy transducer as claimed in claim 5 wherein saidinterface region is defined by at least partially cutting through saiddisc along said diametric portion of said disc.
 7. An ultrasonic energytransducer as claimed in claim 6 wherein said interface region isdefined at least in part by cutting through a central part of said discalong said diametric portion thereof, said central part extendingbetween two opposite edges of an annular ring of said disc which annularring maintains the integrity of said disc.
 8. An ultrasonic energytransducer as claimed in claim 7 wherein said first and second contactsare separate from said annular ring and said contacts further comprisean annular contact substantially corresponding and electricallyconnected to said annular ring.
 9. An ultrasonic energy transducer asclaimed in claim 1 further comprising a support member for supportingsaid piezoelectric element and for restraining movement of said at leastfirst and second portions of said piezoelectric element spaced from saidinterface region.
 10. An ultrasonic energy transducer as claimed inclaim 1 wherein:said piezoelectric element has at least first, second,third and fourth portions, said first and second portions being onopposite sides of said interface portion and being linearly aligned withone another, and said third and fourth portions being on opposite sidesof said interface portion and being linearly aligned with one another,said first and second portions being angularly oriented relative to saidthird and fourth portions; and said electrical contacts furtherproviding for making electrical connection to said third and fourthportions.
 11. An ultrasonic energy transducer as claimed in claim 10wherein said first and second portions are oriented at a 90° anglerelative to said third and fourth portions.
 12. An ultrasonic energytransducer as claimed in claim 1 wherein:said piezoelectric element hasfirst, second, third and fourth portions which interface with oneanother at said interface region, said piezoelectric element comprisinga disc of piezoelectric material, approximately a first quarter of saiddisc defining said first portion of said piezoelectric element andapproximately a second quarter of said disc diametrically opposite tosaid first quarter defining said second portion of said piezoelectricelement, approximately a third quarter of said disc defining said thirdportion of said piezoelectric element and approximately a fourth quarterof said disc diametrically opposite to said third quarter defining saidfourth portion of said piezoelectric element; said interface region ofsaid piezoelectric element comprising a central portion of said discextending between said first, second, third and fourth portions; and,said electrical contacts comprising a first contact electricallyconnected to said first quarter of said disc, a second contactelectrically connected to said second quarter of said disc, a thirdcontact electrically connected to said third quarter of said disc, and afourth contact electrically connected to said fourth quarter of saiddisc.
 13. An ultrasonic energy transducer as claimed in claim 12 whereinsaid contacts comprise an electrode film deposited on said disc, saidelectrode film being removed over said interface region and between saidfirst, second, third and fourth portions of said piezoelectric elementto separate and define said first, second, third and fourth contacts.14. An ultrasonic energy transducer as claimed in claim 1 furthercomprising a support member for supporting said piezoelectric elementand said material contact and wherein said material contact comprises arod rigidly secured by said support member and extending through and adefined distance beyond said piezoelectric element.